1. Field of Endeavor
The invention relates to a turbine of a turbine installation, especially a steam turbine of a steam turbine installation. In addition, the invention relates to a method for the design of a turbine, and also a method for operating a turbine installation which is equipped with such a turbine.
2. Brief Description of the Related Art
On account of the continuing efforts towards improvement of the efficiency of modern turbine installations, especially modern steam turbine installations, it appears desirable to increase the process temperature of the turbine installations. An increase of the process temperature especially has an effect on the high-pressure turbine, on the one hand, and, on the other hand, also on the medium-pressure turbine of the turbine installation, which consequently are exposed to higher temperatures. This leads to temperatures being already achieved today also in steam turbines in which a use of conventional materials, especially for the blading of the turbine, for the flow passage walls and also for the turbine shaft, is no longer possible without temperature reduction measures.
Such a temperature reduction measure, for example, can be to cool the blades of the turbine by means of a cooling fluid. Cooling of blades in gas turbines has already been known for a long time. However, for this purpose, on one hand a cooling fluid is to be made available in a suitable manner, be it by means of an external supply or by means of a bleed from one of the compressor stages of the turbine installation. This leads to a deterioration of the overall efficiency of the turbine installation. Aerodynamic losses are also caused in the case of a film cooling or an effusion cooling of the blades by means of admission of cooling fluid into the main flow of the turbine.
Alternatively, the blades, and partially also the shafts of the turbine, can be produced from high heat-resistant materials, as a result of which, however, the turbine becomes very expensive in production.
In addition to the increase of the process temperature, for the most part, an increase of the process pressure is also sought. By means of the increase of the process parameters there occurs, especially inside the first turbine stages of a high-pressure turbine, only comparatively small volumetric flows of the throughflow fluid which flows through the turbine, mostly air or exhaust gas in gas turbines, as the case may be, or steam in steam turbines.
Small volumetric flows in turn require small blade heights of the turbine blades with small blade aspect ratios. As a result of this, it is often very difficult to design such turbine bladings with a good aerodynamic efficiency.